1. Field of the Invention
This invention relates to a thermal transfer recording sheet which gives lusterless, mat-type printed letters. More particularly, it relates to a thermal transfer recording sheet which give mat-type printed letters, is excellent in the adherence of substrate between ink, and gives a high-quality printed image.
2. Related Art Statement
In recent years, there has been energetically developed thermal transfer recording in which transferred images are formed on ordinary paper by means of a thermal printer, a thermal facsimile telegraph, or the like. The thermal transfer recording are recently widely used, for example, for the following reasons. Since apparatuses for the thermal transfer recording have a simple mechaniam, their maintenance is easy and their prices and maintenance costs are low. The thermal transfer recording permits clear and fast recording by means of low energy. The thermal transfer recording makes it possible to conduct color printing relatively easily by the use of a multicolor ink sheet.
In particular, the amount of consumption of monochromatic type thermal transfer recording sheet is increased owing to the spread of thermal printers for word processor, thermal facsimile telegraphs, etc.
However, images printed by a thermal printer are generally highly lustrous. In the case of multicolor recording, not only precision but also beauty of recording are required, for example, for graphic design and full-color copying, and the gloss of image contributes greatly to these characteristics.
On the other hand, monochromatic printing is often utilized, for example, for printing and duplication of letters. In this case, in reading a printed image, the higher its gloss, the more the eye fatigue of a reader. This is one of points in which the thermal transfer recording is desired to be improved. That is, lusterless mat-type printed letters are eagerly desired.
Under such conditions, as to thermal transfer recording which yields lusterless mat-type printed letters, there are a large number of prior arts.
For example, Jap. Pat. Appln. Kokai (Laid-Open) No. 60-101084 discloses a method in which a matting effect is obtained by subjecting to sandblasting treatment the surface of a base film on which a hot-melt ink layer is to be formed, or by kneading fine particles together with other materials and forming the resulting mixture to a film.
Jap. Pat. Appln. Kokai (Laid-Open) No. 56-164891 discloses a method in which a delustering agent is included in a hot-melt heat-sensitive ink.
Furthermore, Jap. Pat. Appln. Kokai (Laid-Open) No. 60-101083 discloses a method in which a matting layer is formed on a base film.
In addition to them, there is exemplified Jap. Pat. Appln. Kokai (Laid-Open) No. 62-260390 which discloses a dye transfer type thermal printing sheet capable of giving an intermediate tone. This dye transfer type thermal printing sheet comprises a resin A having a high adhesive strength to substrate and a resin B having a low adhesive strength to substrate. In this reference, when the substrate is a polyester film, as the resin A, there is exemplified at least one member selected from the group consisting of saturated polyesters, ethylene-vinyl acetate copolymer resins and silicone resins. And as the resin B, there is exemplified at least one member selected from the group consisting of vinyl chloride-vinyl acetate copolymer resins, vinyl acetate resins, acrylonitrile-phenol copolymer resins and acrylonitrile-styrene copolymer resins. However, the invention of this reference is intended to provide a dye transfer type thermal printing sheet having a high image quality and a high fixability and is characterized in that it was made by noting the fixation due to wear of the printing sheet on an image-receiving sheet after transfer. That is, in the case of the dye transfer type thermal printing sheet of the reference, both the resin A and the resin B are peeled off from the substrate, while a high fixability is imparted. Furthermore, in said reference, an image printed by transfer has an intermediate color tone, and in the examples described in said reference, ink is coated by the use of a solvent in all cases.
The prior arts of the references cited above involve various problems.
For example, the method of subjecting the surface of a base film to sandblasting treatment has defects such as a lowering of the strength of the film itself and a high cost. The method of kneading fine particles together with other materials and forming the resulting mixture into a film is disadvantageous in that a large matting effect cannot be obtained unless a large amount of the fine particles are kneaded together with other materials.
The method of including a delustering agent in ink has the following defect. The delustering agent is generally an inorganic pigment. When it is included in a small amount, a matting effect is difficult to obtain. On the other hand, when it is included in a large amount, the print quality and the transfer density are lowered.
In addition, the method of forming a matting layer on a base film has the following defect. The ink used in the matting layer is a material composed of a binder and an inorganic pigment, and in order to obtain a matting effect, the depth to which the matting effect extends in the matting layer should be increased, so that the particle size or the using amount of the inorganic pigment should be increased.